1. Field of the Invention
The present invention relates to methods of mechanically cleaning pipe, and in particular to methods of cleaning pipe that extends from a tank containing a liquid to a valve, wherein the pipe is cleaned while liquid remains in the tank.
2. State of the Art
It is common in chemical plants to clean piping using a chemical such as an acid. However, to utilize a chemical cleaning method, the piping, tanks and other apparatus associated with the piping must first have all the liquid normally carried by the piping drained from the system. This requires that the piping and associated apparatus must be taken out of operation. The downtime to remove the apparatus from operation is costly. Mechanical cleaning of piping has also been used, but, again, the piping and associated piping has had to be drained of liquid which requires the piping and associated equipment must be removed from normal operation.
The problem with cleaning pipes that connect between a tank and a pump is especially acute. In many pumping applications, a precipitate is formed in both suction and discharge portions of the pipe associated with the pump. As mentioned previously, the precipitate can be removed with acid in some applications. It can also be removed with high pressure water (hydro-blasting). Aside from the problem of downtime associated with acid cleaning and hydro-blasting, another problem with such methods is that the methods are often precluded from being used because of accessibility of the piping, chemical reaction, and product dilution.
Precipitate formation usually occurs most rapidly in areas where laminar flow is disturbed or a temperature change is induced. This is often in the suction area of piping supplying liquid to a pump. A particularly problematic area is the pipe from a tank providing fluid to a pump. Scale will form in the pipe in the area between the tank wall and the valve used to isolate the pump's suction from the tank.
Cleaning the section of piping between the valve and the tank is usually very difficult, especially if attempted while the tank remains filled with its normal liquid contents. Introduction of acid into the section of pipe will dilute the liquid contents of the tank and can be very hazardous in many situations. Further, retention time for the acid in the piping generally does not allow sufficient time for adequate scale removal unless the tank and piping are first drained of their normal contents and acid is allowed to stand or circulate through the tank and piping.
High pressure introduction of fluid into the section of pipe between the valve and the tank has also been suggested. However, the high pressure fluid can only clean a few inches of the section of pipe inasmuch as the resistance of the fluid in the section of pipe reduces the velocity of the high pressure fluid rapidly. In addition, there is no way to check visually to assure that the section of pipe is truly free of scale.
Because of the problems associated with attempts to clean sections of piping between a tank and a valve while the tank remains filled with its normal liquid contents, it has been customary to pump the tank down to a low level. The tank is then physically entered through the side or top of the tank with mobile equipment to remove scale with a mechanical hammer, i.e., a jack-hammer. As mentioned previously, costly downtime is associated with draining, entering, cleaning, closing and re-filling a tank. It would be highly desirable to provide a method of cleaning the sections of piping between a tank and a valve on the suction side of a pump while the tank remains full of its normal liquid contents so as to avoid costly downtime.